Explanation
Given that
[tex]\begin{gathered} A=2x-7x^2+3 \\ B=4x^2-12x \end{gathered}[/tex]We can find A+B by finding the sum of the like terms in the expressions
[tex]\begin{gathered} A+B=2x-7x^2+3+4x^2-12x \\ A+B=2x-12x-7x^2+4x^2+3 \\ A+B=-3x^2-10x+3 \end{gathered}[/tex]Answer:
[tex]-3x^2-10x+3[/tex]